Unit of mass used by chemists and physicists for measuring the masses of atoms and molecules.
Careful experiments have measured the size of this unit;
the currently accepted value (1998) is 1.660 538 73 x 10-24 grams.

In 1959 the national laboratory of Australia, Canada, Great Brittan, New Sealand, USA and South Africa
have decided to define the weight of the pound for precision measurements as:
1 lb = 0,453 59237 kgBefore the
Uklb = 0,453 592 338 kg and the
Uslb = 0,453 592 427 7 kgFor more info see ounce